The present invention relates generally to the field of reciprocating pumps, and more particularly, to a vertical pump that utilizes a stagnant fluid pocket adjacent the piston seal to prevent drilling fluid containing suspended solids from reaching and abrading the seal.
Reciprocating piston pumps are commonly used in drilling applications to extract dense fluid containing suspended solids such as sand, ceramic grit, cement and other debris. Known to those skilled in the art, reciprocating piston pumps are displacement pumps generally including a piston, cylinder, inlet valve and outlet valve. Pumps may include more than one cylinder, and in oil and gas drilling applications, typically include three or four cylinders. During the downstroke or “suction phase,” the inlet valve opens and the outlet valve closes to allow fluid to enter the pump. During the upstroke or “discharge phase,” the inlet valve closes and the outlet valve opens to force fluid from the pump.
Pumps used in drilling applications are required to pump dense fluid over long distances, and therefore operate at pressures up to about 22,000 psi, more commonly from about 10,000-12,000 psi. High pressure causes wear on the pump components, particularly the piston, cylinder and piston seal or “service packing.” The service packing, which is the annular seal disposed tightly between the reciprocating piston and the cylinder wall, is typically constructed from one or more of elastomeric, metal and plastic components. As the piston cycles axially within the cylinder and service packing, pumped fluid containing suspended solids comes into direct contact with the high pressure end of the packing, abrading the packing and consequently degrading the performance of the seal. Worn seals must be replaced on a regular basis, leading to frequent servicing, increased cost and pump downtime.
Accordingly, what is needed is a seal that prevents service packing failure as a result of abrasive wear.